Formation fluid obtained from a reservoir generally contains a number of natural constituents, such as water, super critical gas, and liquid hydrocarbons. In addition to these natural constituents, the composition of the formation fluid may also include contaminants such as filtrate including water-based mud or oil-based mud, used during drilling operations.
Constituents of this formation fluid may be identified by sampling the fluid and then conducting an analysis on the composition of the sampled fluid. The analysis is generally performed by making special measurements of the fluid to characterize the composition and as such infer many properties of interest about the fluid. Knowledge of these properties is useful in characterizing the reservoir and in making many engineering and business decisions.
One type of special measurement that can be made on sampled fluid is density measurements. For example, density measurements are sometimes made at fixed time intervals, and analyzed to estimate the sample's quality. The repeated density measurements can be used to plot the change in density over time. Characteristics of this density-time plot can then be used to assess the composition and contamination level of the sampled fluid. Other types of measurements that can be used in characterizing fluid composition include monitoring density, pressure, temperature and the like.
In addition to making these measurements, various other tools can be used to perform analysis of downhole fluids. For example, spectrophotometers, spectrometers, spectrofluorometers, refractive index analyzers, and similar devices can be used to analyze downhole fluids by utilizing appropriate sensors to measure the fluid's spectral response. Although useful and effective, these types of measurements and tools can be complex to perform and hard to operate in the downhole environment. Moreover, the results of the measurements may not provide the level of detailed information needed to accurately characterize the reservoir.
Though various techniques have been used in the past for characterizing fluid composition of a fluid sample, most of these techniques lack the level of accuracy desired and may also be inefficient. The following disclosure addresses these and other issues.